The present invention relates firstly to a foundation element for supporting a superstructure element on substantially level ground.
In the construction of buildings both by traditional methods of casting reinforced concrete and with the use of prefabricated elements, the foundation elements are, for the most part, also cast by a traditional method.
This method consists of assembling a form on flat, levelled ground, placing the necessary reinforcing bars in the form, including bars which project upwardly for connection to a superstructure element such as a pillar, casting sufficient concrete in the form so as to fill it, awaiting the setting and hardening of the concrete and finally revealing the foundation element by removing the components of the form.
This traditional method is slow and requires a large workforce and is therefore expensive.
Use has also been made of prefabricated foundation elements in the form of monolithic blocks which are also placed on flat, levelled ground. This solution is known, for example, from U.S. Pat. No. 1,474,808. These prefabricated monolithic elements have the disadvantage of being very expensive to transport and move because of their considerable weight and considerable bulk.
Both these known methods require the ground on which the foundation elements are cast or placed to be not only perfectly flat but also perfectly horizontal, which is very expensive.
A first object of the present invention is to provide a foundation element which is much easier and quicker to put into use than prior art foundations and requires only rough levelling and flattening of the ground, all of which considerably reduces the costs of transport and execution.
According to the present invention this object is achieved by means of a foundation element characterised in that it includes a rigid, prefabricated, monolithic frame, including at least two opposite, confining side walls and cross-members interconnecting the two side walls so as to form a casting through-cavity between these walls which, in its condition of use, is downwardly and upwardly open, and in that the frame has adjustable support devices associated with each of the side walls for maintaining these walls at a height above the ground that is adjustable, the monolithic frame being intended to be placed on the ground with the interposition of the adjustable support devices and being intended to receive a settable fluid binder material into its through-cavity, the binder material being able to spill out onto the ground between this and the side walls and to fill the cavity so as to encapsulate the cross-members and iron bars or other connector members for connection to the superstructure element and, after hardening, to constitute a monolithic mass which connects the foundation element and the superstructure element permanently to the ground.
This solution enables a relatively light, monolithic frame for use as a non-recoverable form to be prefabricated, the frame being transportable at little cost from the factory to the construction site and, given its lightness, being movable equally cheaply on site. The ground at the construction site intended to receive the frame needs to be only roughly flattened and levelled since the final levelling of the frame may be achieved after it has been laid by suitable manipulation of the adjustable support devices with the aid of spirit levels or more advanced systems such as modern satellite positioning systems.
In view of the adjustable support devices, a space is left between the levelled framework and the ground through which the fluid concrete or other binder material may spread out of the frame, thereby widening the base for the latter.
The binder material, in spreading out over the ground, adapts to its morphology and ensures an extremely good distribution of the load over the support surface.
After hardening, the frame and the binder material constitute a monolithic foundation element.
Moreover since those surfaces of the foundation element thus formed which are open to view are constituted by parts of the frame, which is prefabricated, these surfaces may have a finished appearance from the start.
As the rigid monolithic frame is itself mechanically strong, it is able to support a superstructure element for an indefinite period of time before its cavity is filled with the binder material.
A foundation element according to the invention enables a method to be carried out, according to the invention itself, for the construction of a prefabricated structure which is characterised by the following operations:
the placing of the rigid monolithic frame of the foundation element on the ground with the interposition of the adjustable support device between the frame and the ground;
the levelling of the frame by adjustment of its support devices;
the connection of the frame and the superstructure element at least by means of a connecting reinforcement fixed, on the one hand, to the superstructure element and, on the other hand, inserted in the frame;
the casting of a hardenable fluid binder material in the cavity in the frame so that this fluid material, after having spread over the ground beneath the frame, fills the cavity of the frame and encapsulates therein cross-members of the latter and the connecting reinforcement;
the hardening of the binder material to obtain a monolithic unit comprising the base element and the superstructure element.
The invention also relates to a prefabricated structure made by this method.
The invention lends itself ideally to the construction of a prefabricated artificial tunnel.
Methods for the construction of prefabricated artificial tunnels on levelled ground constituted by the bottom of a cutting are already known from U.S. Pat. No. 109,886 and EP-A-0 244 890, these tunnels subsequently being covered with earth and being of the type in which the tunnel is formed from consecutive inverted U-sections, each of which includes prefabricated lateral superstructure elements in the form of piers and a prefabricated upper element in the form of an arch resting on the tops of the piers.
In methods known from these documents, the tunnel sections include a prefabricated bed which interconnects the piers as well as the two piers and the arch.
The method of the invention is characterised in that in order to constitute each of the consecutive sections, there is used, in addition to the prefabricated elements in the form of piers and an arch, a pair of foundation elements each of which is of the type claimed, and in that the tunnel section is made by the following operations:
the laying of two rigid monolithic frames on the ground on opposite sides of the bottom of the cutting, each with the interposition of the said adjustable support devices between the frame and the ground;
the levelling of the two frames by adjustment of their adjustable support devices;
the connection of each frame and its pier at least by means of a connecting reinforcement fixed, on the one hand, to the pier and, on the other hand, inserted in the frame;
the casting of a hardenable fluid binder material in the cavity in the frame so that this fluid material, after spreading over the ground beneath the frame, fills the cavity in the frame and encapsulates the cross-members of the latter and the connecting reinforcement;
the hardening of the binder material to obtain a monolithic unit comprising the base element and the pier;
the placing of the arch on the two piers.
This method does not require the use of a prefabricated bed since the two foundation elements do not require prior interconnection to stabilise the structure since they are firmly anchored to the ground.
The tunnel may subsequently be completed by a bed cast by conventional methods, even after the tunnel has been covered with the layer of earth.
The invention also relates to an artificial tunnel made by a method according to the invention and, in particular, to an artificial tunnel characterised in that the piers and the arch are articulated together by joints which each comprise a longitudinal channel of arcuate section and a longitudinal rib of corresponding arcuate section, formed along the adjoining edges of the pier and of the arch, and in that the permanent connecting elements of each articulation are in the form of tie rods which substantially intersect the longitudinal axis of articulation of the joint.
An artificial tunnel which includes couplings having the said configuration and permanent connecting elements is known from EP-A-0 244 890.
In this document, the permanent connecting elements are constituted by tie rods which extend tangentially on the exterior of the structure and which permanently lock the joints so as to prevent mutual pivoting in the finished structure.
This locking of the articulations renders the artificial tunnel according to the document EP-A-0 244 890 unsuitable for use in seismic regions, on unstable ground and where they are subject to unilateral forces resulting from asymmetric external loads, whether permanent or occasional.
The use of tie rods which substantially intersect the longitudinal axis of articulation of the joint however enables an artificial tunnel to be made in which the elements are always articulated together so that they can always pivot relative to each other about the longitudinal axis just as their rotoidal coupling is always ensured, even under the action of external horizontal and sussultatory forces. The tunnel is thus suitable for use in seismic regions or on unstable ground.
Throughout the present description and in the claims, the term xe2x80x9cartificial tunnelxe2x80x9d is used conventionally to indicate a tunnel proper, for example a road or rail tunnel, or a structure with a relatively small section such as a drainage culvert or other underground duct or water conduit or the like.